Endocrine Abstracts

For decades, measurements of the circulating concentrations of GH and IGF1 have constituted a mainstay in the diagnosis and clinical management of GH disorders. However, it is also well-known that considerable discrepancies exist between different assays, resulting in highly assay dependent results. Therefore, in 2009 an International Expert Committee was established with the aim to produce an international consensus statement on the standardization and evaluation of GH and IGF1 assays. The consensus was published in 2011 in Clinical Chemistry (57(4) 555–559) and its appearance will undoubtedly improve the accuracy and precision of the two measurements as well as provide clinically reliable and useful results.

The first part of this session summarizes the obstacles to GH and IGF1 assays and gives an overview on the content of the consensus guidelines, with special emphasis on demands to assay standardization and performance, and collection of reference values.

The consensus guidelines will improve our ability to use IGF1 as a biomarker of many diseases. However, it is important to keep in mind that the assay principle recommended to measure IGF1 only takes the presence of the IGF-binding proteins (IGFBPs) into account to a certain degree. Therefore, our laboratory has developed alternative methods to estimate the endogenous activity of the IGF-system, taking the presence of the IGFBPs into account. Specifically, we have developed a cell-based in vitrobioassay that enables us to compare the physiological and pathophysiological relationship between the IGFBPs, serum levels of IGF1 and the ability of the IGF-system to activate the IGF1 receptor in vitro (i.e. bioactive IGF).

The second part of this session presents examples of clinical situations where a discrepancy exists between the traditional IGF1 measurement and levels of bioactive IGF. This information may be helpful for clinicians when evaluating IGF1 levels in daily clinical practice.